Apparatus for producing electric impulses



Sept. 6, 1966 C, s, 1 KlNGMA ETAL 3,271,624

APPARATUS FOR PRODUCING ELECTRIC IMPULsEs 2 Sheets-Sheet 1 Filed May '7,1964 INVENTOR. CORNELIS S.J. KINGMA PIETER SMID ATTUR/VEY FIB. 2

Sept' 5, 1966 c. s. J. KINGMA ETAL 3,271,624

APPARATUS FOR PBODUCING ELECTRIC IMPULSES Filed May '7, 1964 2Sheets-Sheet 2 FIE'. 3c PIE. 3d

INVENTOR.

CORNELIS S.J.KlNGM/ BY PIETER SMID vwp A 7' TOR/VE Y United StatesPatent O 3,271,624 APPARATUS FOR PRODUCING ELECTRIC IMPULSES CornelisSacharias Johnnes Kingma, Baambrugge, and

Pieter Smid, Haarlem, Netherlands, assignors to Honeywell G.m.b.H.,Frankfurt am Main, Germany, a corporation of Germany Filed May 7, 1964,Ser. No. 365,705 Claims priority, application Germany, May 24, 1963, H49,251 3 Claims. (Cl. 317-81) It is well known to use electricalignition for gas burners. The main advantage of the so-called magnetotype electrical ignition is that electrical connections to a voltagesupply are not required. It is furthermore well known to createelectrical ignition pulses for internal combustion engines byimpact-like mechanical stressing of piezo-electric crystals. Theelectrodes of such piezoelectric crystals are connected to the ignitionplug of the internal combustion engine. A hammer, driven by the enginecam shaft, periodically strikes the piezo-electric crystal so thatelectrical charges are created on the electrodes of the crystal, thechar-ges being used for producing an ignition spark in an electricalcircuit. Also, with such a piezo-electric ignitor no voltage supply isneeded.

The present invention deals with an apparatus for producing electricalimpulses by means of a hammer which applies a sudden impact to apiezo-electric body having electrodes on opposite surfaces. It is anobject of the invention to provide a simple and compact ignitor whichpreferably may be operated manually and in particular is to be used togenerate a spark to ignite gas burner-s. Another object of the inventionis to control the mechanical stress of the piezo-electric body in such amanner that is no destruction of the piezo-electric crystal. Anotherobject is to provide a long life and a reliable operation of theignitor.

According to the invention this is accomplished by providing aself-aligning supporting means for that surface of the crystal which isopposite the surface beaten by the hammer. Because of thisself-alignment, no transver-se forces are supplied to the crystal. Thesupporting means preferably is used as an electrode for the high voltageimpulses.

The invention can be realized by various constructions. According to apreferred embodiment of the invention the supporting means is providedwith a hole shaped like a spherical cap on the side opposite thecrystal. This supporting member is in touch with a ball or a part of aball and can be turned and pivoted with respect t-o this ball. Insteadof a ball-like surface another rotation symmetrical body for instance anellipsoid can be used. In order to have as little friction as possiblebetween the ball-like surface and the spherical cap it is preferablethat these two parts `have a different radius of curvature. Thespherical cap might be replaced by a conical shape. As shown in FIGURE1, the configuration of this supporting means may be such that a ball ora body with ball-like surfaces is located between two supporting memberswith holes of b-all-like or conical shape.

The ball and the spherical cap can also change their places. As shown inFIGURE 2 the plate supporting the piezo-electric crystal is ball-likeshaped on the side opposite the crystal and projects into the hole ofthe supporting member.

Although the provisions las described are concerned with that side ofthe piezo-electric crystal opposite to the hammer, it is of course alsodesired that no transverse forces are supplied to the side of thecrystal which is adjacent to the hammer. In order to meet thisrequirement the impact -of the hammer is transferred to the crystal bymeans of a ball which is guided in a hole on the front of the hammer andis guided by the housing. In order to have an almost equal impactpressure over the whole surface of the crystal a rigid metal plate lieson the crystal and transfers the impact to the crystal. The crystal maybe made of barium titanate or lead-zinc titanate, as examples.

As mentioned above, the hand i-gnitor should be simple and compact. Formeeting this object in accordance with the invention, a helical springfor loading the hammer cc-axially surrounds the crystal `and thesupporting means as shown in FIGURE 2. This helical spring has one endsupported by a flange of a cup like housing which is xed to the hammerand which covers and surrounds the crystal as well as the supportingmeans. The other end of the helical spring abuts against the cover of asecond housing which surrounds the first housing and the helical spring.With a flange of this second housing the ignitor can be mounted to asupporting plate of frame.

It is self-evident that the ignition voltage produced by the ignitorshould be the same with each operation of the ignitor. In order toobtain such a constant ignition voltage in accordance with the inventionthe electrodes of the crystal are discharged automatically before and/orafter every ignition impulse. This provision, which also contributes tothe reliability of the ignitor, can be realized in that a shortingswitch is provided which short circuits the electrodes when the hammeris moved to load the helical spring. The contact lever of this shortingswitch preferably is spring loaded and is automatically closed when thehammer is moved to load its spring. The shorting switch can be operatedby the cuplike first housing surrounding the hammer.

A further method for producing an almost constant ignition voltageconsists in compelling the same spring load of the hammer for everyoperation. This is achieved in accordance with the invention when thehammer is mechanical fixed to a tilting lever which is suddenly pivotedby means of a spring force. The principle of such a tilting leverarrangement corresponds to the principle of the well-known snap actingswitches. According to a preferred embodiment of the invention the oneend of Va tension spring is fixed to the free end of the tilting leverwhilst the other end of the spring is pivotal fixed to an actuatorlever. The pivot of the actuator is chosen in such a manner that duringloading the spring the vector of the spring force passes an unstableposition and therefore effects =a sudden tilting of the tilting lever.The unstable position depends upon the pivot of the tilting lever andupon the working point of the spring. The hammer, which is to strike thecrystal, can be located on the line between the piv-ot of the tiltinglever and the working point of the spring, or on the prolongation ofthis line, or out of this line. An embodiment in accordance with thelast mentioned example is shown in FIGURES 3ft-3d. In these drawings theimpact mechanism of the hammer is shown diagrammatically only.

In order to explain the invention and according features more in detail,reference is made to embodiments of the invention as shown by example inthe drawings.

In the arrangement as shown in FIGURE l a housing 2 covering thepiezo-electric crystal 13 and its supporting means is fixed to thesleeve 1 by means of an inner thread. On the other side of the sleeve asecond housing 3 is fixed to the sleeve and covers the hammer and thehelical spring for actuating the impact. The plunger 4 carries on itsfront end a funnel-like endplate 5 which supports one end of the helicalspring 6. The ball 7 projects into the funnel-like hollow of the plate5. The ball 7, after compression of the spring 6 and release of thehandle 8,

ignitor.

3 lWill strike the steel plate 9 by means of the force off spring 6. Theball 7 is guided within the housing 3. The end of the spring 6 oppositethe ball 7 is supported against the endplate 11 which covers the openingof the cylindrical housing 3.

In the other housing 2 the. piezo-electric crystal 13 and its supportingmeans are located. In referring to the piezo-electric body as a crystait should be mentioned that not only monocrystalline but alsopolycrystalline bodies can be used. The front side of `crystal 13opposite the impact plate 9 lies at upon a supporting part 14 which .isprovided with a spherical hollow 15. Between this supporting part 14.and a symmetrically formed supporting part 16, a ball 17 is positionedso that the supporting part 14, and p-articularly its surface adjacentto the crystal is maintained parallel to the front surface of thecrystal. Connected to the supporting part 16 by means of a pin 19 is thehigh voltage electrode 20 of the A cylindrical insulating sleeve 21 isprovided for electrical insulation between crystal 13, its supportingmeans, and the pin 19 on the one side, and the housing 2 on the otherside. An insulating ring 22 holds the crystal in its radial position. Asthe parts 14, 17, 16, 19 and 20 are of metal they represent theelectrical connection between the high voltage electrode and the onelayer or electrode of the crystal. The impact plate 9, or acorresponding electrode on the adjacent front surface of the crystal,serves as a connection with the housing 2 which usually is grounded. Forfastening the ignitor to the carrier plate or chassis, the sleeve 1 orone of the housings 2 or 3 can be provided with suitable flanges orother mounting means or can be iixed by means of brackets. Whenthreading the housing 2 into the sleeve 1, the end plate 23 and theinsulating bushing 21 press the crystal and its supporting means againstthe impact plate 9 and the spring plate 10. Therefore, the crystal andits supporting means are held under a prestress in their positionrelatively to another. It can be seen that the part of the ball adjacentto the supporting part 14 could also be part of the supporting part 16.In such a case, the supporting part 16 would have -a bal1-likeprojection instead of a spherical or conical hollow. The radii ofcurvature of the ball and of the hollow are different. In the structureas shown in FIGURE l the hollow :has a shape -of -a yconical frustum.

The ball 7 can be rigidly xed to the plunger 4. Then the plate onlyserves as a bearing for the spring 6.

FIGURE 2 shows an embodiment of the invention which is characterized byan especially compact construction. This is achieved by having thehelical spring 36 coaxially surround the crystal 43 and its supportingmeans. After loading the spring by means of the handle 3S, and thenreleasing this handle, the spring force will accelerate the plunger 34in direction to strike the impact plate 39. The plunger 34 is rigidlyiixed to a housing 33 which covers the plunger 34, the crystal 43, andits supporting means. A cylindrical space is provided between theplunger housing 33 and the outer housing 31 which covers the wholearrangement. The helical plunger spring 36 is positioned in thiscylindrical space. The spring has one end engaging the ange 35 of thecuplike inner housing 33 and with its other end engaging the cover plateof the outer housing 31. The spring 36 is loaded by drawing the plunger34 and the lhousing 33 up by means of the handle 38. When the handle 38is released, the plunger 34, with the ball 37 in its front hollow 32,suddenly moves down and strikes the rigid metallic impact plate 39. Thisimpact plate transfers the pressure force to the crystal 43. Both endsurfaces of the cryst-al 43 are ycovered by a brass disc 44. The axialposition of the impact plate 39 and of the crystal 43 with itssupporting means inside the insulating bushing 51 is fixed by means of aspring ring 45 and a spring disc 46. The crystal abutting surface of thesupporting member 47 lies iiatly upon the brass disc 44. The side ofsnap acting switches.

of this supporting member 47 opposite to the crystal is ball-like curved`and projects into a spherical or conical hole of the supporting member4S. Hereby the supporting member 47 is turnable and pivotal with respectto the supporting member 48 and will place itself automatically intoparallel position to the end surface of the crystal 43. By means of aspring disc 46 which abuts against the spring ring 45 the crystal 43together with its supporting means is brought under such a pre-stress sothat no looseness can arise between these parts. Such a looseness woulddecrease the impact force to which the crystal was subjected and therebyred-uce the voltage created at the electrodes of the crystal. Thecomplete ignitor is mounted to the wall 40 by means of a ange 30 ontheoutery housing 31. The front part of the cylindrical insulating body 51which surrounds the conductor pin 49 and bears the high voltage terminal50 projects through a hole in the wall 40. It is secured in thisposition by means of a spring ring 52.

A compulsory discharge of the -crystal 43 before starting a newoperation of the ignitor is effected by means of la shorting switch. Thecontact lever 61 of this switch short circuits the electrodes of thecrystal when the spring 36 is loaded. In the position as shown in FIGURE2, the spring 36 is not loaded. The flange 35 of the cuplike housing 33engages a plunger 62 and pivots the contact lever 61 out of contact withthe high voltage terminal 50. When loading the spring 36, by drawing theplunger 35 to the right, the contact lever 61 will come into contactwith the terminal 50 under the iniluence of spring 63. Thereby thetermin-al 50 is connected electrically to the housing and the crystalelectrodes are discharged. The contact lever 61 is rightangled and theplunger 62 engages the lever 61 in the corner of the lever. The plunger62 projects through an opening in the wall 40. Preferably the Contactlever 61 is part of the spring 63 and is pivotal about an axle 65carried by the bracket 64. The spring 63 and the lever 61 can beseparate parts. The radial position of the crystal is secured by meansof an insulating spacing ring 42.

The voltage created by the crystal depends on the mechanical pressuresupplied to the crystal. It therefore is desired to have the same impactforce with every ignition operation. Such a constant ignition voltage isguaranteed with the aforementioned examples of the invention if theplunger is drawn back to a stop e.g.^to a position Where the spring iscompletely loaded. If then the plunger is suddenly released, the samehigh voltage will be created with every operation. If, however, theplunger is not completely drawn back, or is slowly released, the impactforce supplied to the crystal will be smaller and therefore the ignitionvoltage will also be smaller. In order to avoid this, the inventionprovides a loading and releasing mechanism for the plunger as explainedin the following with respect to FIGURES 3a to 3d. This mechanism isbased on the well `known principle When loading the spring, not only theamount of the vector of the spring force is varied, but also itsdirection is varied so that this vector passes through an unstableposition. After passing through the unstable position, the spring issuddenly released and thereby the striking action is initiated.

As shown in FIGURES 3a to 3d, the plunger or hammer 71 is rigidly fixedto the tilting lever 72. The tilting lever 72 is pivoted about the xedaxle 73. At the end of the tilting lever 72 opposite the pivot 73 atension spring 74 is xed to the free end of a lever 75. This lever, bymeans of a handle 76, can be pivoted about the axle 77. It is an objectof this arrangement that the hammer 71 strike the -crystal 78 suddenly.FIGURE 3a shows the normal position of this arrangement. The springforce of spring 74 presses the tilting lever 72 to the left against thestop 79. If now, by pressing the handle 76 downwards, the lever 75 ispivoted in clockwise direction, the lever 75 goes to the intermediateposition as shown in FIGURE 3b. By doing this the vector of the springforce has increased (the spring has been loaded) and the vectoradditionally has changed its direction. Depending upon the weight andthe distance of the hammer from the tilting lever 72, a definitedirection of the vector of the spring force exists in which the positionof the tilting lever is unstable. It is assumed that this position hasjust been reached in FIGURE 3b. If now the handle is furthermore movedin clockwise direction, the tilting lever 72 suddenly accelerates t-hehammer 71 in the direction of the crystal 78 because of the force of theloaded spring 74. As this action arises at a given angular position ofthe lever 75, and as the spring has reached a given load, the hammer 71strikes the crystal 78 with a given pressure with every operation of thehandle 76. It is of no importance how far the handle 76 is moved inclockwise direction after passing the unstable position. The impactforce is determined only by the spring force when passing the unstableposition. Also, in the end position of the hammer as shown in FIGURE 3c,a residual spring load is present in order to avoid vibrations andfluttering of the hammer with respect to the crystal.

If now the operator releases the handle 76, the force of spring 74returns the lever in a counterclockwise direction as shown by the arrowsin FIGURE 3d. After passing the unstable position, the spring 74 movesthe hammer in counterclockwise direction until it engages the stop 79.During this movement, after passing the unstable position, the hammer 71disengages the crystal. During the movement, before passing the unstableposition, the hammer 71 engages the crystal 78 so that up to this momentonly the lever 75 with the handle 76 and the spring 74 are changingposition. It is obvious that the hammer 71 could also be positioned onthe tilting lever 72, or in the prolongation of the tilting lever 72.The handle need not be rigidly xed to the lever 75. Instead of this aplunger could be used which is pressed from the left side against thelever 75 and thereby pivots the lever in clockwise direction. Theoperation of the impact mechanism would remain the same.

Other modifications of our invention will be apparent to those skilledin the art and we intend that our invention be limited to structures asdefined in the following claims.

We claim as our invention:

1. A piezoelectric spark ignitor, comprising:

a piezoelectric crystal having an axis along which a force is to beapplied to generate a high voltage, said crystal having a pair of endfaces at spaced ends along said axis,

a metallic impact plate mounted to engage one of said end faces andhaving a surface generally normal to said axis,

self aligning support members having mating curved sufaces and having asurface to engage the other of said end faces,

means prestressing said crystal between said plate and said supportmembers,

a hammer having a ball-like member spring biased against said plate andengaging the same at a point,

and switch means actuated by movement of said hammer away from saidplate to short circuit said crystal prior to striking of said plate bysaid hammer.

2. A concentrically arranged piezoelectric spark ignitor for manuallygenerating a spark for use in igniting a gas llame or the like,comprising:

an insulating support member having an open cupshaped recess withmetallic contact means mounted in the bottom thereof, said metalliccontact means having a divergent walled recess formed therein with wallsdiverging toward the opening in said support member,

a metallic crystal support having a ball-like curved surface positionedwithin said divergent walled recess and having a flat surface oppositesaid curved surface,

a piezoelectric crystal, having generally parallel end faces, mountedwithin said support member with one end face engaging the at surface ofsaid crystal support,

a metallic impact plate engaging said other end face of said crystal,

means engaging said impact plate to force said crystal toward the bottomof said support member to prestress said crystal,

a manually movable hammer including a handle and a ball-like surfacewhich engages said impact plate at a point,

a spring concentric with said support member and arranged to bias saidhammer against said impact plate such that movement of said handle awayfrom said plate stores energy in said spring, and release of said handlecause an abrupt impact on said impact plate,

and means adapted to connect said contact means and said impact plate tospark electrodes.

3. A piezoelectric spark ignitor, comprising:

a piezoelectric crystal having generally parallel end faces,

means prestressing said crystal by applying a force to the end facesthereof, said means comprising a gen erally flat impact plate engagingone end face, a self aligning support engaging the other end face, andmeans compressing said crystal between said impact plate and saidsupport,

pivotally mounted hammer means including a ball-like portion to strikesaid impact plate at a point contact,

a pivoted actuating lever for said hammer including an end portion and aspring -connecting said end portion to said hammer, said end portionnormally being positioned to one side of the pivot of said hammer meansto normally bias said hammer away from said impact plate, said actuatinglever being effective upon movement of said end thereof to load saidspring and to move said end portion to the other side of the pivot ofsaid hammer means to thus cause said hammer means to strike said impactplate,

and metallic means adapted to electrically connect said crystal endfaces to ignition electrode means.

References Cited bythe Examiner UNITED STATES PATENTS 2,717,916 9/1955Harkness 123-148 3,200,295 8/ 1965 Owens et al 317-84 3,201,984 8/1965Hinnah et al. 73-141 3,211,949 10/1965 Slaymaker et al 315-55 FOREIGNPATENTS 606,498 10/ 1960 Canada.

966,552 8/1957 Germany. 1,164,141 2/ 1964 Germany.

RICHARD M. WOOD, Primary Examiner. V. Y. MAYEWSKY, Assistant Examiner.

1. A PIEZOELECTRIC SPARK IGNITOR, COMPRISING: A PIEZOELECTRIC CRYSTALHAVING AN AXIS ALONG WHICH A FORCE IS TO BE APPLIED TO GENERATE A HIGHVOLTAGE, SAID CRYSTAL HAVING A PAIR OF END FACES AT SPACED ENDS ALONGSAID AXIS, A METALLIC IMPACT PLATE MOUNTED TO ENGAGE ONE OF SAID ENDFACES AND HAVING A SURFACE GENERALLY NORMAL TO SAID AXIS, SELF ALIGNINGSUPPORT MEMBERS HAVING MATING CURVED SUFACES AND HAVING A SURFACE TOENGAGE THE OTHER OF SAID END FACES, MEANS PRESTRESSING SAID CRYSTALBETWEEN SAID PLATE AND SAID SUPPORT MEMBERS,